This invention relates to an automatic climate control for a vehicle heating, ventilation and air-conditioning (HVAC) system, and more particularly to a method of regulating HVAC control parameters based on an estimate of the heating or cooling power required to maintain the vehicle cabin temperature at a set temperature selected by a vehicle occupant.
In general, an automatic climate control system controls the HVAC control parameters (such as discharge air velocity, temperature and location) based on a desired cabin temperature (referred to herein as the set temperature) and a number of easily measured or estimated parameters such as the outside air temperature, the actual cabin air temperature, and the solar intensity. If the HVAC control parameters are correctly determined, the cabin air temperature will be brought into conformance with the set temperature and then maintained approximately equal to the set temperature despite variations in outside temperature and solar intensity.
Although various methods have been developed for determining the HVAC control parameters, the most physically-based approach is one in which the required heating or cooling effort is estimated based on a thermal loading model for the cabin, and appropriate control parameters for providing the required heating or cooling effort are then selected. The thermal loading model will typically include an ambient component characterizing heat transfer between the cabin and the outside air, a deep mass or core component characterizing heat transfer between the cabin air and the core elements of the cabin (seats, floor mass, etc.), and a solar component characterizing the net solar radiation into the cabin. When the ambient and core temperatures are referenced to the set temperature, the sum of the above-mentioned heat transfer components represents the heating or cooling effort required to maintain the cabin air temperature at the set temperature. In most cases, the required heating or cooling effort may be satisfied by any of a number of different combinations of discharge air temperature and velocity, and the control must include some method of determining which of the potential combinations of discharge air temperature and velocity is most appropriate.
Representative examples of the above-described control approach are disclosed in the U.S. Pat. Nos. 5,400,963 and 5,603,226 to Ishikawa et al., U.S. Pat. Nos. 5,988,517 and 6,173,902 to Bauer et al., and U.S. Pat. Nos. 5,832,990 and 5,995,889 to Eisenhour. Although the controls described in these patents embody a physical basis for determining the required heating or cooling effort under steady-state conditions, the determination of the corresponding discharge air temperature and velocity is time-consuming and/or calculation intensive. Accordingly, what is needed is a simple and efficient method of carrying out a physically based climate control.
The present invention is directed to an improved motor vehicle automatic climate control method which computes the HVAC power requirement for cabin air temperature regulation, and determines corresponding air discharge temperature and blower motor speed commands using a two-step table look-up procedure. Nominal air discharge temperature and blower motor speed profiles are tabulated as a function of a Power Index generally corresponding to ambient temperature, and used along with the set temperature to form a table of HVAC power requirement vs. Power Index. In vehicle operation, the HVAC power requirement vs. Power Index table is used to retrieve a Power Index corresponding to the computed HVAC power requirement, and the air discharge temperature and blower motor speed tables are then used to retrieve air discharge temperature and blower motor speed commands based on the retrieved Power Index. The HVAC power requirement vs. Power Index table may be designed to accommodate different set temperatures, or the table values may be re-calculated during vehicle operation whenever the set temperature is changed.